238	THE RIDDLE  OF LIFE
genes) and each gene is < the cause' of some one unit
quality of the organism which develops from the egg.
The particulate theory in this extreme form was soon
replaced by the view that many genes co-operate in the
production of each distinguishable feature of the adult,
yet (in spite of denials and expostulations from some
quarters) many biologists have continued to write of the
genes as though they, in virtue of their chemical
peculiarities, were the essential active agents in all the
constructive or morphogenetic processes. Thus by one
leading geneticist it has recently been said that the genes
^c control and direct all those chemical reactions which give
rise to all the organs and functions of the body'; that
other genes ' organize and determine intellect '.^1
The influence of genetics in prolonging the life of the
mechanical biology has been very great, partly because a
long series of brilliant discoveries rapidly resulted from
this new method of study, which, accordingly, attracted
many of the ablest students; partly also because these
discoveries quickly bore practical fruit, in the form of
improvements in various breeds of domestic animals and
plants. In this respect biology, for the first time in its
history, began in a small way to rival physical science,
which throughout the nineteenth century had by its
discoveries added immensely to its own prestige by
increasing greatly the wealth of those nations which knew
^1 I cite from Heredity and the Ascent of Man, by C. C.
Hurst (1935), where also it is written : * In the light of the gene
we no longer see through a glass darkly ; the old time problems
of heredity, variation, sex and species appear as clear as crystal.
Experiments have definitely established the fact that the gene
is the primary organizer and determiner of all structural and
functional characters in living organisms.' T. H. Morgan in
1923 wrote of the genes : ^( We must regard the organism in
large part as the outcome of the sum total of their activities.'